An axial gap electric motor may have a rotor which is of squirrel cage or of eddy current design. The squirrel cage design is inherently more efficient since the iron to iron axial gap is smaller than in the eddy current motor. However, squirrel cage motors are generally noisier and have a strong axial attraction between the rotor and stator because of the iron in the rotor. Although in a centrifugal pump this attraction can be more or less balanced at normal speeds by the axial thrust of the impeller carried by the rotor shaft, this does not apply if the motor should run slowly or if it should run dry. Also, in the latter event, the heating of the bearing surfaces in normally employed plain bearings soon causes the motor to break down. Another problem in water pumps driven by squirrel cage motors is corrosion of the iron, and the production of rust and other particles limits the extent to which the axial gap can be reduced.